Adaptive channel equalizer and method for equalizing channels therewith

• US 20070127582A1
• Filed: 12/05/2005
• Published: 06/07/2007
• Est. Priority Date: 12/05/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Sato, Masaki, Lee, Kyu-Man, Zhang, Jun
• Granted Patent: US 7,636,398 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 25/0234 by non-linear interpolation
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

A channel equalizer obtains channel impulse responses (CIRs) for all subcarriers by way of filtering channel impulse responses of specific subcarriers using at least two filters. One of the two filters may be a low pass filter. At least one other of the at least two filters is implemented as a band pass filter having a variable filtering bandwidth, being available to establish various filtering bandwidths in response to various multi-path channel environments. By improving the performance of channel estimation, equalization may be improved.

Claims

1. A method for equalizing channels, comprising the steps of:

generating channel impulse responses in the frequency domain for a plurality of subcarriers of received OFDM symbols;

filtering the channel impulse responses for the plurality of subcarriers by using at least two filters; and

estimating the channel impulse responses for the plurality of subcarriers from outputs of the two filters.

2. The method as set forth in claim 1, wherein in the step of estimating the channel impulse responses, a channel impulse response for a k'"'"'th subcarrier of an l'"'"'th OFDM symbol is given by

${\mathrm{CIR}}_{l.\mathrm{est}}$

( k ) = ∑

p = - L L ⁢

R ^ l ⁡

( k + p ⁢

❘

⁢

( k + p ) ∈

P SP ) } ·

( w cmplxLPF * ⁡

( p ) + w cmplxBPF * ⁡

( p ) ·

ⅇ

- j ⁢

 

⁢

2 ⁢

π

⁢

 

⁢

nk / N ) ,

where;

{circumflex over (R)}_l(k|k ε

P_SP) represents samples of the channel impulse response for the k'"'"'th subcarrier of the l'"'"'th OFDM symbol;

w_cmplxLPF(p) and w_cmplxBPF(p), where p ε

[−

L,L], represent complex coefficients of the two filters;

* denotes the complex conjugate of a complex signal; and

N denotes the number of subcarriers.

3. The method as set forth in claim 2, which further comprises the step of performing a compensation operation for the k'"'"'th subcarrier of the l'"'"'th OFDM symbol by using the estimated channel impulse response.

4. The method as set forth in claim 1, wherein one of the at least two filters is a low pass filter.

5. The method as set forth in claim 4, wherein another one of the at least two filters is a band pass filter.

6. The method as set forth in claim 1, wherein one of the at least two filters is a band pass filter.

7. The method as set forth in claim 6, wherein the filtering bandwidth of the band pass filter is variable.

8. A method of equalizing channels, comprising the steps of:

estimating preliminary channel impulse responses for each of a plurality of subcarriers of an OFDM symbol by using at least two filters;

selecting a subcarrier corresponding with the largest response among the preliminary channel impulse responses;

establishing as the filtering bandwidth of one of the two filters, the bandwidth that corresponds to the selected subcarrier; and

estimating channel impulse responses for each of the plurality of subcarriers by using the two filters.

9. The method as set forth in claim 8, wherein in the step of estimating the preliminary channel impulse responses, a channel impulse response for a k'"'"'th subcarrier of an l'"'"'th OFDM symbol is given by

${\mathrm{CIR}}_{l.\mathrm{est}}$

( k ) = ∑

p = - L L ⁢

R ^ l ⁡

( k + p ⁢

❘

⁢

( k + p ) ∈

P SP ) } ·

( w cmplxLPF * ⁡

( p ) + w cmplxBPF * ⁡

( p ) ·

ⅇ

- j ⁢

 

⁢

2 ⁢

π

⁢

 

⁢

nk / N ) ,

where;

{circumflex over (R)}_l(k|k ε

P_SP) represents samples of the channel impulse response for the k'"'"'th subcarrier of the l'"'"'th OFDM symbol;

w_cmplxLPF(p) and w_cmplxLPF(p), where p ε

[−

L,L], represent complex coefficients in the frequency domain of the two filters;

* denotes the conjugate of a complex signal; and

N denotes the number of subcarriers.

10. The method as set forth in claim 8, wherein, when the subcarrier corresponding to the largest one among the preliminary channel impulse responses is a k1'"'"'th subcarrier, in the step of estimating the channel impulse responses, a channel impulse response for a k'"'"'th subcarrier of an l'"'"'th OFDM symbol is given by

${\mathrm{CIR}}_{l.\mathrm{est}}$

( k ) = ∑

p = - L L ⁢

R ^ l ⁡

( k + p ⁢

❘

⁢

( k + p ) ∈

P SP ) } ·

( w cmplxLPF * ⁡

( p ) + w cmplxBPF * ⁡

( p ) ·

ⅇ

- j ⁢

 

⁢

2 ⁢

π

⁢

 

⁢

nk / N ) ,

where;

{circumflex over (R)}_l(k|k ε

P_SP) represents samples of the channel impulse response for the k'"'"'th subcarrier of the l'"'"'th OFDM symbol;

w_cmplxLPF(p) and w_cmplxBPF(p), where p ε

[−

L,L], represent complex coefficients in the frequency domain of the two filters;

* denotes the conjugate of a complex signal; and

N denotes the number of subcarriers.

11. A method for equalizing channels, comprising the steps of:

receiving OFDM symbols;

generating channel impulse responses in the frequency domain for specific subcarriers of the OFDM symbols;

estimating preliminary channel impulse responses for all subcarriers of the OFDM symbols by using a low pass filter and at least a band pass filter;

selecting a subcarrier in correspondence with the largest one among the preliminary channel impulse responses for all the subcarriers;

establishing as a filtering bandwidth of the band pass filter the bandwidth that corresponds to the selected subcarrier; and

estimating channel impulse responses for the plurality of subcarriers by using the low and band pass filters.

12. The method as set forth in claim 11, wherein the number of band pass filters is two, further comprising the steps of:

selecting the first and second subcarriers corresponding with the first and second largest responses among the preliminary channel impulse responses for the plurality of subcarriers;

establishing as the filtering bandwidth of the first of the two band pass filters, the bandwidth corresponding to the first selected subcarrier; and

estimating channel impulse responses for the plurality of subcarriers by using the low pass filter and the two band pass filters.

13. The method as set forth in claim 12, further comprising:

establishing as the filtering bandwidth of the second of the two band pass filters, the bandwidth corresponding to the second selected subcarrier.

14. The method as set forth in claim 12, wherein the filtering bandwidth of at least one of the band pass filters is established corresponding with the guard interval between received OFDM symbols.

15. The method as set forth in claim 11, wherein a central frequency of at least one of the band pass filters is controlled by e⁻

j2π

nk/N, wherein k denotes an index number of the subcarrier, and N denotes the number of subcarriers.

16. A channel equalizer comprising:

a time-domain interpolator configured to receive OFDM symbols and to generate channel impulse responses in the frequency domain for a plurality of subcarriers of the received OFDM symbols;

a frequency-domain interpolator configured to receive samples of the channel impulse responses from the time-domain interpolator and to estimate channel impulse responses for the subcarriers by using at least two filters; and

a compensator configured to perform a compensation operation for the OFDM symbols through the channel estimation by using the frequency-domain interpolator.

17. The channel equalizer as set forth in claim 16, wherein one of the two filters is a low pass filter and the other of the two filters is a band pass filter.

18. The channel equalizer as set forth in claim 17, wherein the filtering bandwidth of the band pass filter corresponds to a subcarrier having the largest response among estimated channel impulse responses for the plurality of subcarriers.

19. A channel equalizer for an OFDM receiver, comprising:

a time-domain interpolator;

a frequency-domain interpolator including at least two filters; and

a compensator.

20. The channel equalizer as set forth in claim 19, wherein:

the time-domain interpolator is configured to receive a k'"'"'th subcarrier of an l'"'"'th OFDM symbol and to generate channel impulse responses in the frequency domain for a plurality of subcarriers;

the frequency-domain interpolator is configured to receive the channel impulse responses from the time-domain interpolator, and to estimate channel impulse responses for the plurality of subcarriers by using at least the two filters; and

the compensator is configured to perform a compensation operation for the k'"'"'th subcarrier of the l'"'"'th OFDM symbol using the channel impulse response generated by the frequency-domain interpolator.